IS:3177 says that the brake torque should not be more than 200% of the motor torque. The min size of thruster brakes which are available is much more than 200% Also practically seeing also if try to apply brakes on a rotating member with higher torque then the chances are of shearing if the motor shaft Also if the VVVF drives are installed in LT then they should not worry about the type of brake, since brakes are not used for holding and not for breaking. VVVF drives electronically to reduce the motor RPM to zero and then apply the Brakes